Apparatus and method for enhanced heat transfer

ABSTRACT

One embodiment of the system is implemented as a device for two-phase heat transfer. This device comprises a chamber containing a fluid, where a heated wall makes up a portion of the chamber. The device also comprises an actuator that emits pressure vibrations. The pressure vibrations dislodge vapor bubbles that form at the heated wall due to the heat in the wall.

CLAIM TO PRIORITY

The present application claims the benefit of the filing date of U.S.Provisional Patent Application Ser. No. 60/603,436, filed on Aug. 20,2004, which is hereby incorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention is generally related to thermal managementtechnology and, more particularly, is related to an apparatus and methodfor cooling heat-producing bodies or components using a two-phasecooling heat transfer device based on a vibration-induced bubbleejection process.

2. Description of the Related Art

Cooling of heat-producing bodies is a concern in many differenttechnologies. Particularly in microprocessors, the rise in heatdissipation levels accompanied by a shrinking thermal budget hasresulted in the need for new cooling solutions beyond conventionalthermal management techniques. In the microelectronics industry, forexample, advances in technology have brought about an increase intransistor density and faster electronic chips. As electronic packagesincrease in speed and capability, the heat flux that must be dissipatedto maintain reasonable chip temperatures has also risen. Thermalmanagement is recognized as a major challenge in the design andpackaging of state-of-the-art integrated circuits in single-chip andmulti-chip modules.

One method for effective heat transfer is so-called “two-phase” heattransfer. Two-phase heat transfer involves, generally, the evaporationof a liquid in a hot region and the condensation of the resulting vaporin a cooler region. This type of cooling is a highly effective coolingstrategy for at least three reasons. First, the liquid to vapor phasechange greatly increases the heat flux from the heated surface. Second,the high thermal conductivity of the liquid medium, as opposed to thatof air, enhances the accompanying natural or forced convection. A thirdreason for the efficient heat transfer that occurs during two-phase heattransfer is that buoyancy forces remove the vapor bubbles generated atthe heated surface away from the heated surface.

Two-phase, or “boiling,” heat transfer is known and has been studied fora number of years. Heat pipes and thermosyphons are examples ofefficient heat transfer devices that have been developed to exploit thebenefits of two-phase heat transfer. Immersion cooling, which involvesthe pool boiling of a working fluid on a heated surface, is anotherexample of a two-phase cooling technology.

There are limitations to the current state of the art in two-phasecooling. First, two-phase heat transfer systems have traditionally beenviewed as incompatible with microelectronic packages. This is largelydue to the fact that liquid is involved in the process.

Second, two-phase heat transfer systems are constrained by a phenomenathat manifests itself most noticeably in microgravity environments. Whenthe heat flux from the surface is increased past a critical level, alarge, potentially catastrophic increase in temperature occurs. Thiscritical heat flux marks the transition from nucleate boiling to what isknown as film boiling. In film boiling, a thin insulating layer of vaporcompletely covers the heated surface, which then produces a largetemperature increase. This transition occurs at much lower heat fluxesin a microgravity environment because buoyancy forces are almostnegligible. Thus, the performance of immersion cooling in thisenvironment is drastically reduced.

A heretofore unaddressed need exists in the industry to address theaforementioned deficiencies and inadequacies.

SUMMARY

Embodiments of the present invention provide a system and method forcooling heated bodies and environments by using a vibration-inducedbubble injection system, method, and device.

A cooling cell based on the submerged vibration-induced bubble ejection(VIBE) process in which small vapor bubbles attached to a solid surfaceare dislodged and propelled into the cooler bulk liquid capitalizes onthe benefits of two-phase cooling while improving on traditional methodsof implementing two-phase heat transfer. The VIBE device described belowexceeds the performance of conventional immersion cooling devicesbecause it delays the onset of the critical heat flux. By forciblyremoving the attached vapor bubbles with pressure instabilities, theVIBE device and method dissipate more energy for a given surfacetemperature than previous immersion coolers.

Briefly described, in architecture, one embodiment of the VIBE devicedescribed herein, among others, can be implemented as a device fortwo-phase heat transfer. This one embodiment comprises a chambercontaining a fluid. This embodiment also comprises a heated wall makingup a portion of the chamber. Finally, the embodiment comprises anactuator that emits pressure vibrations. The pressure vibrationsdislodge vapor bubbles forming at the heated wall due to the heat in thewall.

Embodiments of the present invention can also be viewed as providingmethods for cooling. In this regard, one embodiment of such a method,among others, can be broadly summarized by the following steps: (i)providing a chamber with a fluid; (ii) generating heat in a wall of thechamber; (iii) causing the formation of vapor bubbles at the heatedwall; and (iv) emitting pressure vibrations into the fluid, wherein thevapor bubbles dislodge from the heated wall due to the pressurevibrations.

Other devices, systems, methods, features, and advantages of the presentinvention will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional devices, systems, methods, features,and advantages be included within this description, be within the scopeof the present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the invention can be better understood with reference tothe following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present invention. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a cut-away side view of a first embodiment of a two-phase heattransfer device.

FIG. 2 is a cut-away side view of an alternative embodiment of anactuator used in a two-phase heat transfer device.

FIG. 3 is a cut-away side view of a second embodiment of a two-phaseheat transfer device.

FIG. 4 is a cut-away side view of a third embodiment of a two-phase heattransfer device.

FIG. 5 is a cut-away side view of a fourth embodiment of a two-phaseheat transfer device.

FIG. 6 is a cut-away side view of a fifth embodiment of a two-phase heattransfer device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present disclosure is directed to a method and apparatus for heattransfer. The cooling method and apparatus described herein generallyuse a two-phase cooling heat transfer device based on avibration-induced bubble ejection (“VIBE”) process.

Construction of the Vibe Device

FIG. 1 depicts a first embodiment 10 of an apparatus for accomplishingthe disclosed method through the use of a VIBE cooling apparatus. TheVIBE apparatus 10 of the first embodiment generally comprises a chamber11 for holding a fluid 12.

The chamber 11 could be constructed of any suitable material. Generally,the material used for the chamber 11 will depend to some degree on theparticular fluid 12 in the chamber 11 and on the particular heattransfer characteristics desired. The preferred material from which thechamber 11 is to be constructed is a light-weight metallic material fromwhich the chamber 11 can be easily and inexpensively manufactured. Forexample, the material for the chamber 11 of the present embodiment 10 isaluminum.

In the present embodiment 10, the entire chamber 11 is constructed froman aluminum material. However, in an alternative embodiment, the chamber11 is manufactured from more than one material. In other words,different parts of the chamber 11 are manufactured from differentmaterials. Such a configuration minimizes heat transfer to certain partsof the chamber 11, while maximizing heat transfer to other parts of thechamber 11.

More specifically, in this alternative embodiment, some parts of thechamber 11 are constructed from a highly thermally conductive material.Other parts of the chamber 11 are constructed from a thermallyinsulating material. This possibility will be discussed morespecifically below.

Generally, the chamber 11 may be manufactured in any shape desired ordictated by the use to which the VIBE apparatus 10 will be put. One ofordinary skill in the art will easily be able to size and shape anappropriate chamber 11 for a given application. In the presentembodiment 10 the chamber 11 is cubic. The cubic chamber 11 has a lowerwall 13, an upper wall 14, and two side walls 15, 16. Of course, thechamber 11 also comprises a front wall and a back wall. As FIG. 1 is acut-away side view of the present embodiment 10, the front wall is notdepicted in FIG. 1.

As will be explained in more detail below, the fluid 12 in the chamber11 of the VIBE device 10 will be involved in a heat transfer process.For this reason, the selection of the fluid 12 to be used with the VIBEdevice 10 may change depending on the particular application of thedevice 10. As will be readily understood by one of ordinary skill in theart after reading this description, different fluids will exhibitdifferent heat transfer, safety, availability, and othercharacteristics. After reading the present description, one of ordinaryskill in the art would easily be able to make an appropriate fluidselection.

The fluid 12 in the present embodiment 10 is a mixture of methanol andwater. The preferred mixture of the present fluid 12 is 70% distilledwater and 30% methanol. However, the fluid 12 of the present embodiment10 does not have to comprise such a mixture.

For example, if more viscosity in the fluid 12 is desired, ethyleneglycol, or an ethylene glycol/water mixture, is used as the workingfluid 12 of the device 10. Alternatively, 100% distilled water could beused of the working fluid 12 of the present embodiment 10. Almost anyfluid could be used in the VIBE device 10, depending on the particularapplication of the device 10 and the particular performancecharacteristics desired. Generally, it has been found that lowerviscosity fluids are preferred for most applications. Lower viscosityfluids in the VIBE device 10 generally permit greater heat transfer and,thereby, a greater cooling effect. In most applications, greater coolingis desired.

In the present embodiment 10, the chamber 11 is preferably hermeticallysealed except for an inlet pipe 17 and an outlet pipe 18. These twopipes 17, 18 permit the fluid 12 to flow into and out of the chamber 11,respectively. Preferably, a fluid flow is established in the chamber 11by moving fluid into the chamber 11 through the inlet pipe 17, therebyforcing fluid 12 out of the chamber 11 through the outlet pipe 18. Ofcourse, the fluid flow could also be established in the chamber 11 bywithdrawing fluid 12 through the outlet pipe 18, thereby creating apressure gradient that draws fluid 12 into the chamber 11 through theinlet pipe 17. Although described in the present embodiment, a fluidflow in the chamber 11 is not required for the VIBE device 10 tofunction properly. Alternative embodiments of a VIBE device without afluid flow will be discussed in more detail below.

The fluid flow described above is created in the present embodiment 10because the inlet pipe 17 and outlet pipe 18 are both part of aconnected fluidic system, as depicted in FIG. 1. In the presentembodiment, the pipes 17, 18 are fluidically connected to a fluidreservoir 19 and/or a remote heat exchanger. The fluid 12 is caused toflow into the chamber 11 though the inlet pipe 17, and out of thechamber 11 through the outlet pipe 18. The outlet pipe 18 carries thefluid 12 to the fluid reservoir 19, where the fluid 12 is circulatedback into the inlet pipe 17 and carried back to the chamber 11. Ofcourse, the fluid reservoir 19 of the present embodiment 10 is notrequired for the VIBE device to function. In some embodiments, the fluidreservoir 19 can be omitted.

In an alternative embodiment of the present VIBE apparatus 10, thedevice includes a process for cooling the fluid 12 while the fluid 12 isin, or passing through, the reservoir 19. This is preferablyaccomplished by the fluid reservoir 19 taking the form of a container ina refrigerated cabinet. Alternatively, the reservoir 19 is equipped withother means of refrigeration. In either configuration, heat is directlyextracted from the fluid 12 in the reservoir 19 by an external coolingmechanism.

In an alternative embodiment, the fluid reservoir 19 takes the form of aheat exchanger remote to the chamber 11. In this alternative embodiment,the fluid 12 is cooled as it moves through the fins of the remote heatexchanger.

Preferably, a pump 21 is affixed at the fluid reservoir 19 in order tomove the fluid 12 from the fluid reservoir 19 through the inlet pipe 17back to the chamber 11. Basically, the pump 21 is the apparatus of thefluid system that actually creates the desired fluid flow in the chamber11.

The VIBE device 10 of the present description does not require that apump 21 be used to circulate the fluid 12 through the fluid system.Indeed, if a fluid flow is desired, the fluid 12 may be moved throughthe pipes 17, 18 and chamber 11 in a variety of ways consistent with thepresent embodiment 10. For example, fan blades, louvers, or other fluidmovement apparatus may be used to move the fluid 12 through the system.In addition, the type and size of pump 21 of the present embodiment 10may be altered in order to increase or decrease the fluid flow rate asdesired for a particular application. One of ordinary skill in the art,upon reading the present description, can readily select and implement apump 21 of the appropriate size and configuration.

The present embodiment 10 also includes an actuator 22 situated in thechamber 11. The actuator 22 is mounted to the upper wall 14 of thechamber 11. Alternatively, the actuator 22 could be manufactured intothe structure of a wall of the chamber 11. This alternative design willbe discussed in more detail below.

The actuator 22 of the present embodiment 10 can be of many possibledesigns. However, the depicted actuator 22 comprises a diaphragm 23secured to a mounting body 24 (or simply a “mount”).

The diaphragm 23 is preferably constructed of a ceramic material with acopper or brass layer; however, this particular construction is notrequired. The diaphragm 23 is preferably securely attached to the mount24. The diaphragm 23 may be attached to the mount 24 by any appropriatemeans, and the particular method of attachment is not critical to thepresent embodiment 10.

In the depicted embodiment of the actuator 22, the mount 24 ispreferably cubic in shape. The diaphragm 23, therefore, is formed into asquare shape such as to form one wall of the mount's cube shape.

Attached to an inner side of the diaphragm 23 is a piezoelectric element26. The piezoelectric element 26 is preferably attached to the diaphragm23 by an adhesive, or other means. The piezoelectric element 26 isactuated by a discrete electronic driving circuit 27 of this embodimentthat is preferably positioned exterior to the chamber 11. The drivingcircuit 27 comprises a sinusoidal function generator and anamplification chip (not separately depicted in FIG. 1). The drivingcircuit 27 is electronically connected to the piezoelectric element 26by appropriate wiring 30 that passes through the upper wall 14 of thechamber 11.

The mount 24 is preferably constructed of a lightweight metal, such asaluminum. The cubic shape of the mount 24 of the present embodiment isnot required. Indeed, the mount 24 could be formed into, for example, acylindrical shape. In this situation, the diaphragm 23 is manufacturedinto a circular shape in order to correspond to the cross-section of themount 24. The shape of the mount 24 and the diaphragm 23 are notcritical to the functioning of the VIBE apparatus 10.

An alternative configuration of the actuator 22 positions the drivingcircuit 27 inside the mount 24. FIG. 2 is a cut-away side view of thisalternative actuator 22 configuration. In such a configuration, thedriving circuit 27 is placed inside the mount 24 such that the actuator22 is completely self-contained.

As briefly mentioned above, the actuator 22 of a second embodiment 35 isbuilt into a wall of the chamber 11. See FIG. 3. For example, thediaphragm 23 of the actuator 22 could be positioned flush with, or atleast closer to, the upper wall 14 of the chamber 11. This embodimentfor a VIBE device 35 is depicted in FIG. 3. In this configuration, themount 24 is entirely exterior to the chamber 11.

In another alternative embodiment 40, the mount 24 is completelyeliminated and the diaphragm 23 forms one of the chamber walls 14. Thisconfiguration 40 is depicted in FIG. 4, which is a cut-away side view ofthis third embodiment 40. In such a configuration 40, the upper wall 14of the chamber 11 is comprised of a diaphragm 23. The driving circuit 27is positioned on a side wall 16 of the chamber 11. The diaphragm 23 isstill equipped with a piezoelectric element 26 that is driven by thedriving circuit 27.

Returning to FIG. 1, the bottom wall 13 of the chamber 11 is adjacent toa heated body or heat-producing body 28. For example, a microelectroniccircuit or chip may be situated adjacent to the bottom wall 13 of thechamber 11. Thus, the heat from the heat-producing body 28 travels intothe bottom wall 13 of the chamber 11. As will be apparent to one ofordinary skill in the art, the material that forms the bottom wall 13 ofthe chamber 11 affects the rate of heat transfer into this wall 13. Asnoted above, the preferred material for all the walls of the chamber 11is aluminum. Since the preferred bottom wall 13 is constructed ofaluminum, the heat transfer into the wall 13 will be at a relativelyhigh rate.

In an alternative embodiment, the bottom wall 13 of the chamber 11 isconstructed of a different material from the remainder of the chamber 11in order to increase heat transfer into the bottom wall 13, but reduceheat transfer into the other walls of the chamber 11. The bottom wall 13of the chamber 11 in this alternative configuration is constructed ofcopper, but the other walls of the chamber 11 are constructed of a lessthermally conductive material, such as aluminum, brass, or mostpreferably plastic.

Regardless of the material making up the walls of the chamber 11, theconfiguration of the VIBE device 10 is modified in other alternativeembodiments. For example, in one other alternative embodiment, thebottom wall 13 of the chamber 11 is positioned next to a larger heatsink structure. With such an embodiment, the heat sink absorbs heat fromone or more heat-producing bodies. Then, the VIBE device would removeheat from, and consequently cool, the heat sink.

In another alternative embodiment, a heat-producing body actually formsthe bottom wall 13 of the chamber 11 itself. Basically, a housing of amicroelectronic circuit makes up at least a portion of the bottom wall13 of the chamber 11. In this alternative embodiment, the VIBE device 10directly cools the heat-producing device itself.

Operation of the Vibe Device

In operation, the VIBE apparatus 10 functions to cool the heated body28. As the heated body 28 produces heat, the heat flows into the bottomwall 13 of the chamber 11. The heat is further transferred into thecooler fluid 12. As the fluid 12 absorbs heat, the temperature of thefluid 12 adjacent to the bottom wall 13 rises. At some point in time,the temperature of the fluid 12 adjacent to the bottom wall 13 willreach the boiling temperature of the fluid 12. Upon the fluid 12reaching its boiling temperature, vapor bubbles 29 will begin to form atthe bottom wall 13 of the chamber 11. In essence, the fluid 12 beginsboiling.

Initially, the vapor bubbles 29 tend to cling to the bottom wall 13 ofthe chamber 11. If the VIBE device 10 was is not operating, the vaporbubbles 29 continue to cling to the bottom wall 13 as the temperature ofthe wall 13 and the adjacent fluid 12 continues to rise. As thetemperature of the fluid 12 adjacent to the bottom wall 13 continues torise, a critical temperature is reached where nucleate boiling of thefluid 12 generally ceases and film boiling begins. This critical pointvaries depending on the fluid 12 used. In this situation, the vaporbubbles 29 begin to form a thin insulating layer of vapor along thebottom wall 13 of the chamber 11. If this were allowed to continue,there would be a dramatic reduction in cooling of the bottom wall 13,and consequently, the heated body 28.

The present VIBE device 10, however, remedies this potential limitationby causing the actuator 22 to vibrate the diaphragm 23. The vibration ofthe diaphragm 23 creates a series of pressure waves 31 that emit fromthe diaphragm 23. The waves 31 strike the bottom wall 13 and cause thevapor bubbles 29 to become dislodged. Once dislodged, the buoyancy ofthe vapor bubbles 29 carry them up and away from the bottom wall 13 ofthe chamber 11. At this point, the fluid flow discussed above sweeps thevapor bubbles 29 away from the bottom wall 13 and out of the chamber 11.Once away from the bottom wall 13 of the chamber 11, the vapor bubbles29 begin to cool. As the bubbles 29 cool, they condense, release theirstored heat into the surrounding fluid 12, and are thus reincorporatedinto the fluid 12. In this manner, the heated bottom wall 13 of thechamber 11 is cooled. In turn, this process cools the heated body 28.Basically, the action of the VIBE device 10 in dislodging the vaporbubbles 29 prevents the formation of the thin insulating layer of vapordiscussed above, and prevents reaching the critical heat flux in whichthe surface is coated with vapor.

Preferably, the diaphragm 23 of the present embodiment 10 is caused tovibrate at its resonant frequency of its first axisymmetric mode ofvibration. Nominally, this frequency in the first embodiment is about1.65 MHz. Vibration of the diaphragm 23 at this frequency producesultrasonic pressure waves in the fluid 12. It is not necessary tovibrate the diaphragm 23 at its resonant frequency, but this ispreferred. This is because ultrasonic pressure waves 31 are alsopreferred, though not required.

An alternative embodiment of a VIBE apparatus 50 is depicted in FIG. 5.As will be seen in the figure, this embodiment 50 comprises no inflowpipe and no outflow pipe. The chamber 11 is completely sealed. In thisembodiment 50 the bubbles 29 that are released from the bottom wall 13of the chamber 11 move away from the bottom wall 13 and into coolerfluid 12, which causes the bubbles 29 to condense. This embodiment 50 ofa VIBE apparatus has the advantage of being self-contained and smaller.This embodiment 50 can be used as a portable device to be attachedwherever heat removal and/or cooling is needed. However, the heatremoval capacity and rate may not be as efficient as that of the firstembodiment 10.

An alternative embodiment of a VIBE apparatus 60 is depicted in FIG. 6.This embodiment 60 is very similar to the previous embodiment 50.However, small synthetic jet actuators 61, 62 have been placed withinthe chamber 11. Synthetic jet actuators, generally, are described indetail in U.S. Pat. No. 5,758,853 to Glezer et al., entitled “SyntheticJet Actuators and Applications Thereof,” which is incorporated herein byreference. Basically, the synthetic jet actuators 61, 62 create jets 63,64 of fluid without net mass injection into the chamber 11. The fluidicjets 63, 64 agitate the fluid 12 in the chamber 11 resulting in moreeffective heat transfer.

Other alternative embodiments of the VIBE device involve modificationsof the actuator 22. One of these alternative embodiments involves usingmore than one actuator 22 in the chamber 1. An array of actuators ispositioned along the upper wall 14 of the chamber 11. In anotheralternative embodiment, the actuator 22 comprises a mount and a pistonsystem in order to create the pressure waves 31.

It should be emphasized that the above-described embodiments of thepresent invention, particularly, any “preferred” embodiments, are merelypossible examples of implementations, merely set forth for a clearunderstanding of the principles of the invention. Many variations andmodifications may be made to the above-described embodiment(s) of theinvention without departing substantially from the spirit and principlesof the invention. All such modifications and variations are intended tobe included herein within the scope of this disclosure and the presentinvention and protected by the following claims.

1. A device for cooling a heated object, comprising: a chambercontaining a fluid; a heated wall comprising a portion of said chamber;and an actuator, said actuator emitting pressure vibrations fordislodging vapor bubbles from a surface of said heated wall.
 2. Thedevice of claim 1, wherein said fluid comprises water.
 3. The device ofclaim 2, wherein said fluid further comprises methanol in addition towater.
 4. The device of claim 1, wherein said actuator comprises anultrasonic actuator and said pressure vibrations comprise ultrasonicpressure waves.
 5. The device of claim 1, wherein said actuatorcomprises: a diaphragm; a piezoelectric element attached to saiddiaphragm; and a circuit for driving said piezoelectric element, saiddriving circuit comprising a sinusoidal function generator and anamplification chip.
 6. The device of claim 5, wherein said diaphragmcomprises a ceramic disk.
 7. The device of claim 1, wherein said chamberfurther comprises: an inflow pipe at a first wall of said chamber, saidinflow pipe in fluid communication with an interior of said chamber; anoutflow pipe at a second wall of said chamber, said outflow pipe influid communication with an interior of said chamber; and wherein saidfluid in said chamber moves out from said chamber through said outflowpipe and into said chamber through said inflow pipe.
 8. The device ofclaim 7, further comprising: a reservoir in fluid communication withsaid chamber via said inflow pipe and said outflow pipe, said reservoircontaining said fluid.
 9. The device of claim 1, wherein said heatedwall comprises a heat sink material.
 10. The device of claim 9, furthercomprising a heat-producing object adjacent to said heat sink material.11. The device of claim 10, wherein said heat-producing object comprisesa microelectronic circuit.
 12. The device of claim 1, wherein saidheated wall comprises a portion of a microelectronic circuit.
 13. Thedevice of claim 1, further comprising a synthetic jet actuator in saidchamber.
 14. A method for cooling, comprising the steps of: providing achamber with a fluid; generating heat in a wall of said chamber; causingthe formation of vapor bubbles at said wall of said chamber; emittingpressure vibrations into said fluid; and said vapor bubbles dislodgingfrom said wall of said chamber due to the pressure vibrations.
 15. Themethod of claim 14, further comprising the step of circulating saidfluid through said chamber.
 16. The method of claim 15, wherein saidemitting step comprises the steps of: providing an actuator, saidactuator having a diaphragm; vibrating said diaphragm at a resonantfrequency of said diaphragm; and causing pressure waves to move throughsaid fluid from said diaphragm, said pressure waves impinging upon saidwall.
 17. The method of claim 14, further comprising the steps of:providing a fluid reservoir, said fluid reservoir in fluidiccommunication with said chamber; moving said fluid from said chamber tosaid reservoir and back to said chamber; and cooling said fluid in saidreservoir.
 18. The method of claim 17, wherein said moving stepcomprises: providing a fluidic pump; and pumping said fluid from saidfluid reservoir to said chamber, and from said chamber back to saidfluid reservoir.
 19. A cooling device, comprising: a chamber containinga fluid a heat source supplying heat into said fluid of said chamber;and an actuator for emitting pressure vibrations into said fluid. 20.The device of claim 19, wherein said heat source comprises a wall ofsaid chamber.
 21. The method of claim 20, wherein said actuatorcomprises a diaphragm vibrating at a resonant frequency of saiddiaphragm.